1. Field of the Invention
The present invention relates to a ball bearing and a supporting construction therefor, and more particularly to a ball bearing for use in an automotive transmission or the like in which lubricating oil is fed from an axial direction for forcibly lubricating the ball bearing and a supporting construction therefor.
2. Description of Related Art
Ball bearings are assembled to an automotive transmission in which lubricating oil is fed from an axial direction for forcible lubrication.
Conventionally, there has been known a ball bearing having a cage which includes: an annular portion; pillar portions which extend in the axial direction from a plurality of circumferential locations of the annular portion and which form pocket portions for retaining balls as rolling elements therebetween; and an inclined portion which is inclined in the axial direction so as to constitute a small diameter at an axially central side thereof is formed on an inner circumferential surface of the annular portion and which extends substantially over the full width thereof (for example, JP-A-2005-90692).
In addition, as the conventional forcibly lubricated ball bearing, there has also been known a ball bearing in which balls are retained at intervals between an outer ring and an inner ring by a cage so as to be interposed rotatably between the outer ring and the inner ring, and the cage is a machined cage which is formed by cutting a ring material and in which one axial end face is formed larger in outside diameter than the other axial end face and an outer circumferential surface is formed into a tapered surface which is downwardly inclined from the one axial end face towards the other axial end face (For example, JP-UM-A-5-96548).
In addition, in the ball bearings built in a device of a vehicle such as a motor vehicle, a radial clearance resulting in a state that the ball bearings are built in the device is set to 20 μm or less from the viewpoints of rigidity, vibration and life (for example, JP-A-2003-49837).
The ball bearing disclosed in the above patent application is a pulley unit ball bearing which is built in a pulley unit of a motor vehicle and in which a rotational shaft of a pulley is fittingly inserted in an inner ring thereof, and a radial clearance resulting in a state that the ball bearing is built in the device is set to be in the range of −10 μm to 7 μm.
Incidentally, in conjunction with the recent tendency that more and more attentions are paid to environmental issues, there is an increasing demand for reduction in torque required to rotate a ball bearing which makes up a transmission of a motor vehicle.
In the ball bearings described in the patent application documents referred to above, however, since the lubricating oil is allowed to flow smoothly into the bearing by forming the inclined surface on the inner circumferential surface of the outer circumferential surface of the cage, the lubricating oil tends to flow into the bearing more than required. As a result, the drag torque is increased by virtue of the resistance of the lubricating oil that so flowed into the bearing, and the dynamic frictional torque of the bearing is increased by the drag torque so increased, which constitutes a barrier to enhancement in transmission efficiency of the transmission of the vehicle.
On the other hand, in the event that the feeding amount of lubricating oil is reduced in order to reduce the drag torque caused by the resistance of the lubricating oil, there is caused a fear that the thickness of a lubricating oil film becomes insufficient to thereby reduce the life of the bearing, and in the worst case, there is a concern that seizing of the bearing is generated. In addition, in a case where a lubricating oil feeding path is shared by the ball bearing and other peripheral parts, the effect resulting from reducing the feeding amount of lubricating oil is propagated to the peripheral parts, causing a possibility that the feeding of lubricating oil becomes so insufficient that the lubrication of the peripheral parts is badly affected. In addition, in the event that a crown cage is used as the cage, there is caused a problem that the lubricating oil fed to the bearing is agitated largely by not only the balls but also tabs to thereby increase the oil agitation loss.
In addition, in the ball bearing including the crown cage, pairs of tab portions which are formed on an axial end face of the crown cage agitate lubricating oil which flows into the bearing, whereby the oil agitation loss of the bearing is increased.